Microbial activity hotspots of organic matter mineralization stabilized on goethite

Minerals such as goethite play a crucial role in protecting soil organic carbon (SOC) from microbial mineralization through the formation of mineral-organic associations via adsorption and/or precipitation processes. Additionally, goethite can promote the development of aggregates and Fe-organic complexes that contribute to the stabilization of rhizodeposits-derived carbon (rhizo-C). However, at the microscale, the effects of goethite on soil microbial communities and carbon sequestration remain poorly understood. In this study, we investigated two levels of initial soil iron oxide content (Fe 10% and Fe 20%) with the aim of quantifying the impact of goethite on root exudate mineralization and sequestration, as well as identifying microbial hotspots at these two concentrations. This was accomplished through isotopic natural abundance labeling techniques. The results indicate that the addition of goethite facilitated the sequestration of carbon derived from rhizodeposits within microaggregates and clay-silt fractions. Furthermore, it enhanced populations of copiotrophic microorganisms residing in macroaggregates while increasing areas characterized by heightened microbial activity. These findings underscore the importance of goethite in inter-root carbon dynamics and contribute to our understanding of carbon-iron-microbial interactions within hotspot regions.